iStock/Thinkstock(THE HAGUE, Netherlands) -- The operation to remove all of Syria's declared chemical weapons reached a major milestone on Monday as the final batch was turned over for destruction.

"With this last movement, the total of declared chemical weapons materials destroyed or removed from Syria has reached 100%," the Organization for the Prohibition of Chemical Weapons (OPCW) said in a statement.

Along with the removal of all the declared weapons, the organization said Syria has "destroyed all declared production, mixing and filling equipment and munitions, as well as many buildings associated with its declared chemical weapons programme."

Only 12 production facilities remain, according to the OPCW, pending a decision by the organization's executive council.

OPCW Director-General Ahmet Uzumcu said in an announcement on Monday that the removal of the last of the Syrian chemical weapons was "a major landmark."

While in Iraq Monday, Secretary of State John Kerry acknowledged the accomplishment.

"I want to congratulate the UN-OPCW Joint Mission and the entire international coalition, which operated under very dangerous conditions to remove more than 1,000 tons of declared chemical weapon materials from Syria," Kerry said.

But he noted that the work in Syria is not finished, adding, "We remain deeply concerned about the reports of systematic use of chlorine gas in opposition areas."